1. Field of the Invention
The present invention relates generally to the field of double-walled storage tanks, and more specifically, to double-walled storage tanks having a pressure relief vent.
2. Statement of the Problem
Double-walled storage tanks are well known in the art for a wide variety of uses. In recent years, double-walled storage tanks have increasingly been used for above-ground storage of gasoline and other flammable liquids. In order to enhance safety, such double-walled tanks typically have a pressure relief vent to prevent the buildup of an excessive pressure within the tank by venting the interior of the tank to the atmosphere when the internal pressure exceeds a predetermined limit. However, when such tanks are transported on the bed of a flat-bed truck or other vehicle, the liquid within the tank surges due to changes in the relative velocities of the truck and tank with respect to the liquid contained within the tank. The surging liquid can impinge on the pressure relief vent, and the dynamic pressure of the surging liquid can cause the vent to open even though the static pressure within the tank has not reached the predetermined limit. The pressure relief vent typically remains open once triggered. The open vent may not be noticed by the driver of the vehicle for quite some time. While the open vent goes unnoticed, the fluid will continue to surge out of the open vent, creating a particularly dangerous problem in the case of flammable liquids. Therefore, a need exists for an apparatus to prevent the surging liquid within a double-walled tank from causing the pressure relief vent of the tank to open.
A number of devices have been invented in the past to prevent liquids from surging out of passageways to tanks. However, none of these devices were for use on a double-walled tank with a pressure relief vent. These prior art devices include the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Dedman 2,918,192 Dec.22, 1959 Runo 3,128,899 April 14, 1964 Frederick 967,895 April 23, 1910 ______________________________________
Dedman discloses an anti-splash venting closure for the circular filler neck of a fuel tank for a gasoline powered mower or the like.
Runo discloses a vent for use with fluid storage tanks in which fluid within the tank is drained by means of a suction force applied to a discharge opening in the tank.
Frederick discloses a breather for a crankcase of an engine to relieve pressure, the breather having baffle plates to allow free passage of air but to prevent oil from being splashed out of the crankcase.
3. Solution to the Problem
None of these prior art references show a double-walled storage tank with a pressure relief vent and means between the pressure relief vent and the liquid in the tank to prevent the liquid from impinging against the pressure relief vent. More specifically, none show a cover with a pressure relief vent and a deflection surface mounted to the cover to prevent the fluid from directly impinging against the vent causing it to open. Instead, all of these prior art references concern devices providing a continuous, constantly open path between the external atmosphere and an interior volume. Hence, these devices would not work in conjunction with a passageway sealed by a cover having a pressure relief vent where the passageway was intended to be sealed except when the internal pressure exceeded a predetermined limit, at which limit the pressure relief vent would open to vent the interior volume to the atmosphere surrounding the tank.
The present invention provides a novel, relatively low cost, and rugged solution to the stated problem by providing a double-walled tank having a passageway from an inner tank to an outer tank, the passageway having an outer opening, and a cover removably mounted over the outer opening of the passageway to seal the passageway. The cover has a pressure relief vent and a plate suspended from the cover, within the passageway, below the pressure relief vent, and above the opening in the inner tank. In the event of liquid surging within the tank, the plate prevents the liquid from impinging against the pressure relief vent. In addition, in order to prevent tampering with the pressure relief vent, the cover has an enclosure around the pressure relief vent to prevent tampering.